This invention relates to a liquid crystal display (will be abbreviated to an LCD hereinafter) device with wide viewing angle and, in particular, to a method of subjecting alignment films included in the LCD device to an aligning treatment.
In general, LCD devices have various advantages that they are thin in thickness and low in power consumption, and so on, in comparison with CRT (cathode ray tube) display devices. Therefore, such LCD devices might be expected to be substituted for CRT display devices and have been a matter of great interest in some industry fields.
However, LCD devices are disadvantageous in that a viewing angle is narrow as compared with the CRT display devices. Taking this into consideration, various schemes have been devised to widen the viewing angle of the LCD devices.
As one of recent schemes, proposal has been made about an In-Plain Switching mode (IPS) of an LCD device so as to widen the viewing angle of LCD devices. It is to be noted that such an LCD of an IPS type is based on a principle different from ones of other types, such as Twisted Nematic (TN) mode, Super Twisted Nematic (STN) mode, and the like, that will be collectively referred to as a usual LCD device. In this connection, the LCD device of the IPS type will be called a new LCD device.
With regard to the usual LCD device, it is known that an electric field is vertically impressed relative to a principal surface defined by a substrate. When such an electric field is selectively and locally impressed on a liquid crystal layer, liquid crystal molecules in the liquid crystal layer are vertically aligned or oriented relative to the principal surface. Coexistence of aligned liquid crystal molecules with normal liquid crystal molecules brings about contrast between black and white on the usual LCD device.
On the other hand, the new LCD brings about the contrast by horizontally and locally impressing an electric field parallel to a principal surface. In this case, the liquid crystal molecules of the liquid crystal layer are locally aligned or oriented along the parallel electric field. More specifically, each liquid crystal molecule represented by an oval shape model is rotated in a plane due to the parallel field. This results in rotation of an orientation vector of each liquid crystal molecule defined by a long axis of each molecule. Herein, the orientation vectors of the molecules are termed directors. At any rate, it is known in the art that the new LCD device can decrease dependency of the viewing angle, as compared with the usual LCD device. Specifically, such dependency of the viewing angle is representative of a relationship between the viewing angle and the contrast.
As one of the new LCD device, an LCD device is disclosed in Japanese Unexamined Patent Publication No. Hei 9-80436, namely, JP-A 9-80436 and will be called a conventional LCD device. The conventional LCD device has a first substrate with a first principal surface and a second substrates with a second principal surface opposite to the first principal surface. On the first substrate, first and second electrodes are deposited which have particular shapes like combs and which are alternately arranged with each other in an interleaved manner. The conventional LCD device, furthermore, has a liquid crystal layer formed by a plurality of molecules which are interposed and sealed between the first and second substrates. Specifically, splay alignment must be carried out such that pretilt angles of the liquid crystal molecules fall within a range between 0 and 1.5 degrees, both inclusive, in the conventional LCD device. The conventional LCD device of such structure should theoretically exhibit a wide viewing angle and a high contrast.
However, the above-mentioned LCD device cannot practically accomplish a good yield in a conventional production process. When the conventional LCD device is designed and manufactured in accordance with the conventional technique, undesirable light points partially appears on the conventional LCD and result in occurrence of an inferior article. Therefore, the yield becomes low. This makes the cost of the LCD device high. Such a conventional LCD device of a high cost is undesirable in the consumer market, even if regular or normal products have wide viewing angles.